1. Field of the Invention
This invention relates generally to internal combustion engine spark ignition systems, and in particular to an ignition coil module that contains a ferromagnetic core about which primary and secondary coils are coaxially disposed. The ignition coil module may be a type that mounts on an engine over, and in direct electric connection with, an engine-mounted spark plug, in the manner of modules referred to by various names such as pencil-coil modules or coil-on-plug modules.
2. Background Information
Known internal combustion engines comprise cylinder blocks containing individual cylinders that are closed at one end by an engine cylinder head that is attached to the engine block. In a spark-ignition engine, the cylinder head contains threaded spark plugs holes, each of which is open to a respective cylinder. A respective spark plug is threaded into the respective hole to close the respective hole. External to the respective cylinder, each spark plug comprises a central electric terminal that is available for electric connection with a mating terminal of a secondary of the spark-ignition system.
Known spark ignition systems comprise what are sometimes called coil-on-plug type ignition coil modules or pencil-coil modules. Any such module comprises both a wound primary coil and a wound secondary coil. At the proper time in the engine operating cycle for firing a particular spark plug, electric current flowing through the primary of the respective module is abruptly interrupted to induce a voltage in the secondary coil sufficiently high to create a spark across gapped electrodes of the spark plug that are disposed within combustion chamber space of the respective engine cylinder, igniting a combustible fuel-air mixture to power the engine.
Examples of coil-on-plug modules are found in various patents including U.S. Pat. Nos. 4,514,712; 5,128,646; 5,590,637; and 5,870,012; as well as in U.K. Patent Application GB 2,199,193A. A common characteristic of such modules is that the primary and secondary coils are disposed one within the other, concentric with a common axis that is coincident with the spark plug central terminal. The coils may be bobbin-mounted and encapsulated. Various arrangements for providing electric circuit continuity of the secondary coil to the spark plug terminal are shown.
In certain engines, the threaded spark plug mounting hole may be at the bottom of a bore, or well, that extends inward from an outer surface of a cylinder head. For any of various reasons, such bores may be relatively long and narrow, and it is for such bores that pencil-coil ignition modules are especially suited. U.S. Pat. No. 6,094,122 xe2x80x9cMECHANICAL LOCKING CONNECTION FOR ELECTRIC TERMINALSxe2x80x9d, pending U.S. patent application Ser. No. 09/391,571 xe2x80x9cPENCIL IGNITION COIL ASSEMBLY MODULE ENVIRONMENTAL SHIELDxe2x80x9d, and pending U.S. patent application Ser. No. 09/392,047 xe2x80x9cPENCIL IGNITION COIL ASSEMBLY MODULExe2x80x9d disclose an example of such a module.
An advantage of a pencil-coil module is that when it is installed on an engine, the wiring that runs to it from a signal source need carry only primary coil current, because the entire secondary coil is contained within the module and is for the most part sheltered within the bore. However, for proper ignition system performance, primary and secondary coils must be sized to reliably deliver a secondary voltage sufficiently large to spark the plug. The primary and secondary coils are typically encased in respective encapsulations which must possess physical characteristics suitable for providing protection both for the harsh underhood environment where an ignition coil module is located and for the voltages that must necessarily be generated. Because of dimensional constraints imposed by the design of an engine on a pencil-coil module, it is believed that a module possessing an ability to achieve specified performance criteria within confined space would be valuable to an engine manufacturer. It is further believed that the pencil-coil module shown in U.S. Pat. No. 6,094,122 and the two referenced pending patent applications possesses such value, and that further improvements can increase the value of such a product.
The present invention relates to improvements in an ignition coil module, especially improvements in the ferromagnetic core of the module and the manner in which the core is associated with a bobbin within which the core is coaxially disposed. It is believed that improved efficiencies in the fabrication and performance of ignition coil modules will result from use of the inventive principles disclosed hereinafter. While the inventive improvements can provide particular benefit in a module like the pencil-coil module of U.S. Pat. No. 6,094,122, they may also enjoy application to other ignition coil modules.
The improvements can enable a core to be efficiently assembled into a bobbin and to attain precise coincidence of the core centerline to the bobbin centerline. Effectively encapsulating the core within the bobbin is also an aspect of the invention. The core and bobbin employ features relating one to the other in an assured dimensional relationship that allows encapsulant that is introduced into the open upper end of the bobbin to flow efficiently into the bobbin interior and fill clearance space that is intentionally provided between the outer surface of the core and the inner surface of the bobbin. This results in a construction that is believed more robust because of the improved thermal/mechanical isolation provided between dissimilar materials in the bobbin and the core. A substantial surface area of the core is spaced from the wall of the bobbin, and the intervening space filled by encapsulant. Because of that construction, it is believed that thermal and mechanical factors acting on the module while in use may have less of an effect on design intent than they would absent the present invention.
The construction also allows additional magnetic circuit elements, such as magnetic cylinders, to be associated with the core within the bobbin interior. A retainer associates with the open upper end of the bobbin to keep the core, including any additional magnetic circuit elements associated with the core within the bobbin, in place before encapsulant is introduced, yet the retainer possesses features that allow encapsulant to flow efficiently past it as the encapsulant is introduced into the bobbin. When an additional magnetic circuit element is placed over a core that has been inserted into the interior of a bobbin, the retainer may also serve to dimensionally center that additional magnetic circuit element to the centerline of the core.
The present invention relates to a pencil ignition coil assembly module that possesses an organization and arrangement of elements believed to render it well suited for meeting specified performance criteria within the confines of limited space. Moreover, it is believed that the inventive module is well suited for reliable and cost-effective mass production, thereby making it especially attractive for use in automotive vehicle internal combustion engines.
One general aspect of the invention relates to an ignition coil module having an imaginary longitudinal centerline and comprising a primary coil for conducting primary electric current, and a secondary coil that is electromagnetically coupled with the primary coil for delivering a spark plug firing voltage when primary current conducted by the primary coil abruptly changes. A bobbin comprising an imaginary centerline is disposed coincident with the module centerline and comprises a sidewall having an inner surface that laterally bounds a hollow interior space and an outer surface on which one of the coils is disposed. A ferromagnetic core is disposed within the interior space of the bobbin and has a longitudinal centerline coincident with the centerlines of both the module and the bobbin. The core comprises an outer surface having a confronting area which confronts and is spaced from a confronted area of the inner surface of the bobbin sidewall, and the confronting area of the outer surface of the core and the confronted area of the inner surface of the bobbin sidewall are disposed on respective imaginary frustums having their centerlines coincident with the centerlines of the core and the bobbin.
Another general aspect relates to an ignition coil module having an imaginary longitudinal centerline and comprising a primary coil for conducting primary electric current and a secondary coil that is electromagnetically coupled with the primary coil for delivering a spark plug firing voltage when primary. current conducted by the primary coil abruptly changes. A bobbin comprising an imaginary centerline is disposed coincident with the module centerline and comprises a sidewall having an inner surface that laterally bounds a hollow interior space and an outer surface on which the secondary coil is disposed. A ferromagnetic core is disposed within the interior space of the bobbin and has a longitudinal centerline coincident with the centerlines of both the module and the bobbin. The core comprises an outer surface having a confronting area which confronts and is spaced from a confronted area of the inner surface of the bobbin sidewall, and encapsulant fills the interior space of the bobbin between the confronting area of the outer surface of the core and the confronted area of the inner surface of the bobbin sidewall.
Another general aspect relates to a ferromagnetic core having an imaginary longitudinal centerline and comprising a stack of individual flat laminations arranged parallel to the centerline. Two of the laminations bound the stack. Each lamination comprises opposite longitudinal edges that are non-parallel to the centerline to endow zones at opposite sides of the core with a substantially frustoconical profile, and the zones are separated by flat outer faces of the two laminations bounding the stack.
Another general aspect relates to a ferromagnetic core having an imaginary longitudinal centerline running from a proximal end to a distal end and comprising a stack of individual flat laminations arranged parallel to the centerline. Two of the laminations bound the stack. Each lamination comprises opposite longitudinal edges that endow opposite sides of the core with zones that have a defined longitudinal profile and that are separated by flat outer faces of the two laminations bounding the stack. Some of the laminations comprise tabs projecting outward from their longitudinal edges beyond the defined longitudinal profile.
Another general aspect relates to an ignition coil module having an imaginary longitudinal centerline and comprising a primary coil for conducting primary electric current and a secondary coil that is electromagnetically coupled with the primary coil for delivering a spark plug firing voltage when primary current conducted by the primary coil abruptly changes. A bobbin comprising an imaginary centerline is disposed coincident with the module centerline and comprises a sidewall having an inner surface that laterally bounds a hollow interior space and an outer surface on which one of the coils is disposed. A ferromagnetic core is disposed within the interior space of the bobbin and has a longitudinal centerline coincident with the centerlines of both the module and the bobbin. The core comprises an outer surface having a confronting area which confronts and is spaced from a confronted area of the inner surface of the bobbin sidewall. A retainer fits to the proximal end of the bobbin to capture the core within the bobbin. The retainer comprises a ring that is disposed within the interior space and comprises formations that provide clearance to the bobbin sidewall to allow encapsulant that is introduced into the interior space via the proximal end of the bobbin to flow past the retainer and fill the interior space between the confronting and confronted areas.
Another general aspect relates to a method of encapsulating a ferromagnetic core within a bobbin of an ignition coil module. The method comprises providing a bobbin comprising a sidewall having an exterior surface on which one of a primary and a secondary coil is disposed and an interior surface bounding a hollow interior space that is open at a longitudinal end. A ferromagnetic core is disposed within the hollow interior of the bobbin via the open longitudinal end of the bobbin to circumferentially locating the core to the bobbin and to place an imaginary longitudinal centerline of the core coincident with an imaginary longitudinal centerline of the bobbin. The core is captured within the bobbin by disposing on the bobbin at the open longitudinal end, a retainer that has a cooperation with the bobbin allowing encapsulant to flow past the retainer. Encapsulant flows into the interior space of the bobbin to encapsulate the core by introducing the encapsulant through the open longitudinal end of the bobbin and flowing the encapsulant past the retainer.